Blasting the official electoral watchdog, the Guardians Council, the Assembly of Qom Seminary Scholars and Researchers said it no longer had the "right to judge in this case as some of its members have lost their impartial image in the eyes of the public."
On Tuesday, the unelected 12-member council upheld the re-election of hardline incumbent Mahmoud Ahmadinejad over complaints of fraud from his challengers that had brought hundreds of thousands out onto the streets.
Government spokesman Gholam Hossein Elham is a council member.
The reformist clerics said the council "did not pay attention" to the complaints lodged by defeated candidates Mir Hossein Mousavi and Mehdi Karroubi.
"The voice of people seeking justice was marred by violence which unfortunately left several dead and wounded and hundreds arrested," they said.
"How can one accept the legitimacy of the election just because the Guardians Council says so? Can one say that the government born out of these infringements is a legitimate one?"
The clerical group from Qom, the clerical nerve-centre of Iran, is a pro-reformist body seen as a counter to the conservative Qom Seminary Scholars Association.
The reformist clerics urged the authorities to release those arrested in post-election protests.
